Process for producing alpha-aminobenzylpenicillin

ABSTRACT

THE PRODUCTION OF A-AMINOBENZYLPENICILLIN IN A BIPHASIC SOLVENT SYSTEM COMPRISING A WATER IMMISCIBLE HALOGENATED HYDROCARBON AND WATER PROVIDES AN IMPROVED METHOD OF SYNTHESIS IN THAT BETTER YIELDS ARE OBTAINED AND A SMALLER VOLUME OF WATER, WHICH MUST LATER BE REMOVED, IS USED.

3,649,625 PROCESS F OR PRODUCING a-AMINOBENZYL- PENICILLIN Leon John Heuser, Robbinsville, and Carl Francis Anderson, Milltown, N .J., assignors to E. R. Squibb & Sons, Inc., New York, N.Y. No Drawing. Filed Nov. 12, 1969, Ser. No. 876,111 Int. Cl. C07d 99/14 US. Cl. 260-2391 6 Claims ABSTRACT OF THE DISCLOSURE The production of tx-aminobenzylpenicillin in a biphasic solvent system comprising a water immiscible halogenated hydrocarbon and water provides an improved method of synthesis in that better yields are obtained and a smaller volume of water, which must later be removed, is used.

BACKGROUND AND SUMMARY OF THE INVENTION Various processes for the production of a-aminobenzylpenicillin, a wide spectrum antibiotic, in its various forms have been described. One process involves the reaction of the N-carboxy anhydride of phenyl glycine with 6- aminopenicillanic (6-APA) acid in an aqueous acidic medium. It has also been disclosed that 6-aminopenicillanic acid may be purified by treating an impure aqueous solution thereof with an amine of more than six carbon atoms and an aldehyde of more than four carbon atoms, recovering the amine salt of the Schifis base formed thereby and converting this to purified 6-aminopenicillanic acid.

It has now been found that an improved process for the production of a-aminobenzylpenicillin results when the reaction product of 6-aminopenicillanic acid (6-APA) with certain aromatic aldehydes, especially in the form of a tertiary alkyl amine salt, is treated in a biphasic solvent system comprising water and a water immiscible halogenated hydrocarbon with the N-carboxy anhydride of phenylglycine. This new process provides a number of advantages. It obviates the need to purify 6-APA. Better yields are obtained. The water medium, which later must be removed, is used in much less volume.

DETAILED DESCRIPTION OF THE INVENTION According to this invention a-aminobenzylpenicillin is produced by reacting the product formed from 6-aminopenicillanic acid, preferably in the form of a tertiary alkyl amine salt, and a reactive aromatic aldehyde, not including an a-hydroxy group, with the N-carboxy anhydride of phenylglycine in a biphasic solvent system comprising water and a water immiscible chlorinated alkane of not more than three chlorine atoms on a single carbon. The aldehyde reaction product is soluble in the organic solvent phase and the final product is soluble in and is recovered from the aqueous phase.

Reactive aromatic aldehydes which form an imine reaction product with 6-APA or its salt include benzaldehyde or simply substituted benzaldehydes wherein the phenyl group bears a methylenedioxy group, one to two halogens, especially chlorine or bromine, a lower alkoxy group, e.g., methoxy (which is preferred), ethoxy, etc. a.-Hydroxy groups are excluded. Illustrative aldehydes in addition to benzaldehyde are p-anisaldehyde, mor p-chlorobenzaldehyde, piperonal, and the like.

Preferably the 6-APA used in this reaction is in the form of a salt formed with a tertiary alkyl amine in which the tertiary alkyl group has about 7 to 10 carbon "ited States Patent 0 3,649,625 Patented Mar. 14, 1972 atoms, like t-octylamine, t-nonylamine or the like, especially the first.

To form the biphasic solvent system a water immiscible chlorinated alkane of not more than four carbon atoms is used. There are no more than three chlorines on a single carbon. These include, for example, methylene chloride, which is preferred, chloroform, trichloroethylene, ethylene dichloride and the like.

The amount of water immiscible chlorinated hydrocarbon solvent used in the biphasic solvent system is about 30 to 70% the amount of water (v./v.), although under most circumstances approximately equal volumes of the two solvents give best results.

The reaction of the aldehyde-6-APA reaction product with the N-carboxy anhydride is best effected at an acid pH in the range of about 4 to 6, preferably about 4.5-5.5 and at a temperature just above the freezing point of water, e.g., in the range of about 1-l5 C.

According to the preferred embodiment, a tertiary alkylamine salt of 6-APA, especially the t-octylamine salt, is reacted with the aromatic aldehyde, preferably benzaldehyde or anisaldehyde, in an aqueous solution, preferably at a pH of 6.0-9.0. The reaction product readily crystallizes from solution even when a solution of crude 6-APA is used as the starting material.

Then the reaction product of the aldehyde and 6-APA in the salt form, is dissolved in a mixture made up of approximately equal volumes of water and chlorinated hydrocarbon, especially methylene chloride, cooled to about 1 to 5 C. The aldehyde reaction product, which dissolves in the organic phase, is used in an amount approximately 0.1-0.2 molar with respect to the organic solvent. The pH is adjusted, e.g., with hydrochloric acid, to about 4.5 to 5.5. The N-carboxy anhydride of phenyl glycine, in an amount approximately equimolar in proportion to the aldehyde-6-APA reaction product, is added. After the reaction is complete, the insolubles are separated by filtration or centrifugation. After separation of the aqueous from the organic phase, the a-arninobenzylpenicillin product is recovered from the water phase.

Not only does this procedure result in superior yields of product, but, since the starting materials are soluble in the organic phase and the final product is soluble in the aqueous phase, recovery of the product is facilitated. A further advantage lies in the ability to use smaller amounts of water as solvent in relation to the final product, while still obtaining yields comparable with other processes. Since recovery of the product from the aqueous phase entails concentration of the water, the use of lesser amounts of water in what is a relatively dilute system provides obvious advantages in the recovery of the product on an economically feasible basis.

It will be appreciated that the final product occurs in optically active forms or racemic mixtures thereof which are traceable to the use of the D-, L- or racemic form of phenylglycerine and that all such forms are within the scope of this invention.

The N-carboxy anhydride may be formed for example by treating phenylglycine with phosgene in an inert solvent such as toluene, dioxane or tetrahydrofuran and isolating the product by concentration with hexane.

The following examples are illustrative of the invention. All temperatures are expressed on the Centigrade scale. It will be appreciated that the L-form or racemic forms may be substituted for the optically active starting materials used by way of illustration below.

EXAMPLE 1 To 750 ml. of 6-APA hydrolysate (an aqueous mixture obtained in the enzymatic hydrolysis of penicillin G) at pH 8.0 (Est. 24.0 gms. 6-APA) are added 108 ml. of an aqueous tertiary octylamine hydrochloride solution (ca.

3 50% octylamine by weight). 25.5 ml. of benzaldehyde are added. A crystalline slurry forms and the pH drops to 6.3-6.5. The pH is maintained in the range 6.3-6.5 for two hours using tertiary octylamine. The mixture is stored hydrate is washed with 10 ml. of cold water, then with 15 ml. acetone and air-dried. Yield: 3.1 gms. (85 'y/mg. bioactivity) EXAMPLE 3 at a I for two hours The fibenzyfidene'aminopenicil' 5 The i eronal derivative of 6-APA-t-octylamine salt is lanic acid as the t-octylamine salt is filtered OE and the substituting piperonal for benzaldehyde in the crystals are washed with 75 ml. of water, then 75 ml. Procedure of Example L toluene Yield (F]0nmemc.aSs.ay981.'Y/mgJ' 15.0 gms. of this salt is slurried in cold methylene 125 D'OL'phenylglyCme slurned m met i chloride (1 C.) and cold water (250 ml. of each). The i g and warmed. to Phosgene ggc g' pH is adjusted to 4.8 with 1:1 HCl. 5.7 grams of N-cara i to aiemperature. boxy anhydride of D-phenylglycine chloride in 40 ml. of The addition is continued until the solution clears (2 methylene chloride over a Period of 20 minutes The hours 10 minutes) and nitrogen is passed through to action is continued for one additional hour at lad-4.9 and excess. i i a temperature of 1 C. The mixture is then centrifuged. 1 gg f q gg g i unlder lg m The aqueous supernatant liquid is decanted oil" and the g an m e s ig i p insolubles are washed with water and the wash is added fi f a ig 0 minutes 6 S 18 ept to the main fraction. The methylene chloride is removed 3 m the co room 1 hour. 5 than m6 crysta s from the aqueous portion and this solution is neutralized are filtered and washed with an additional 200 ml. hexane. to PH 43 with sodium hydroxide and Stored at 0 for g g ig ig i gg g gg igi f under vacuum over Phos' one hour. The insolubles are filtered oil (500 mgs.). The p A p l d 5 aqueous filtrate is concentrated to 90 ml. and stored at 1 rfmxture 9 3 j g g g on 3 5 C. overnight. The crystalline precipitate is filtered, i3 0 C .1 "i Washed with 15 ml. of cold water and 30 ml. of acetone. 1 ene amlnopenlcl. acld as t e t'octy amine Sat a Yield: 7.3 gm. of 6-D-a-aminobenzylpenicillin trihydrate. addmon of 9' benzaldehyde. The following data illustrate the improved results obtu.re adjusted to wlth 18% hydrochloric acid tained by the process of this invention. The first part of the mmutes) of N'cahboxyanliydnde of phenylglycme table below shows the yield of 6-D-a-aminobenzylpeniare added and the reaction continued for 5 minutes at cillin m-hydrate when the N carboxy anhydride of 3:; i g g gf f i f i ggg i g i g fig gi phenylglycine is reacted with 6-APA-benzylidene-t-octylp g y e e amine salt by the procedure of Example 1 utilizing the sol- Over a penod Inmates and the roeacnon vent system indicated. The second group of data show ture stirred for an additional 1 hour at 1-3 C. and pH the yields obtained by reacting the Nwarboxy anhydride 47-49 of D-phenylglycine with 6-APA in similar solvent systems.

TABLE Solvent (5) Yield 0! product Starting material Wt. (gms.) Type (mL Wt. (gms.) Percent (l) G-APA-benzylidene-tOA 15 H20 250 2.75 19.5 (2) G-APA-benzylidene-tOA 1!! H20 500 2. 96 21 a G-APA-benzylldene-tOA 15 {Ea 528} 1.1 45.8 (4) G-APA 7.5 H30 250 2.95 21 (5) fi-APA 7.5 H20 450 3.6 21.5 (e) B-APA 7.5 {55 ,3 ggg 2.1 15

The insolubles (0.9 g.) are removed by centrifugation The above data demonstrate that the reaction of the and the layers are separated. The aqueous layer, after 50 aldehyde reaction product in either 250 or 500 ml. of wastorage for 1 hour at 5 C. is filtered. ter alone gives 19.5% and 21% yields, respectively. In a The aqueous filtrate is then concentrated under vacuum mixed solvent system comprising 250 ml. each of water and to about 110 ml. and allowed to stand at 5 C. overmethylene chloride the yields increase markedly to 48.5%. night. The crystalline product is filtered, washed with When 6-APA alone is used in either water or a mixed solcold water and acetone and air dried. Yield: 7.1 g. 6-D-mvent the yields are 21%, 27.5% and 15%, respectively. aminobenzyl-penicillin trihydrate (829 'y/mg. bioactivity). No marked difference is evident between experiments 1, EXAMPLE 2 2, 4, 5 and 6, but there is a significant difierence in the results obtained in Experiment 3. 6-APA-anisylidene-t-octylamine salt is formed by substi- What is claimed is: tuting anisaldehyde for benzaldehyde in the procedure 1. A process for the production of a-aminobenzylpeni of Example 1. To 7.5 gms. of 6-anisylidene-APA-t-octylcillin which comprises reacting the product formed from amine salt are added 100 ml. of cold methylene chloride 6-aminopenicillanic acid or tertiary alkyl amine salt there- (1 C.) followed by 100 ml. of cold water. Then 0.3 ml. of and benzaldehyde or substituted benzaldehyde wherein of anisaldehyde are added. A slurry forms and this mixthe henzaldehyde substituent is other than a-hydroxy ture is adjusted to pH 4.8 (1:1 HCl). 2.86 gms. of the group with the N-carboxyl anhydride of phenylglycine in N-carboxy anhydride of D-phenylglycine are added over a bisphasic solvent system comprising about 30% to a period of V2 hour, maintaining the temperature and by volume of water and about 70% to 30% by volume of pH range of 4.8-4.9 during the reaction. The mixture is a water immiscible chlorinated alkane of not more than slurried for 1 hour after the N-carboxyanhydride is added. four carbon atoms and not more than three chlorine atoms The mixture is centrifuged and the supernatant is sepa- 70 on a single carbon, and separating the product from the rated. The insolubles are washed with 20 ml. of water, aqueous phase. centrifuged and the wash is added to the main aqueous 2. A process as in claim 1 wherein the aromatic aldefraction. The aqueous layer (pH 4.8) is concentrated to hyde is benzaldehyde. one half its original volume and stored at 5 C. over- 3. A process as in claim 1 wherein the aromatic ald night. The crystalline 6-D-u-aminobenzylpenicillin trihyde is anisaldehyde.

4. A process as in claim 2 wherein the tertiary amine References Cited salt is t-octylamine and the chlorinated alkane is methyl- UNITED STATES PATENTS ene chloride 3 206 455 9/1965 Alburn et al 2602391 5. A process as in claim 3 wherein the vtertiary amine salt is t-octylarnine and the chlorinated alkane is methyl- 5 3248387 4/1966 Album et 26o 239'1 fine chloride NICHOLAS s. RIZZO, Primary Examiner 6. A process as in claim 4 wherein the amount of methylene chloride is about 50% by volume of solvent US. Cl. X.R.

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